1. Field of the Invention
The present invention relates to an image sensor, and more particularly, to an image sensor that increases the diameter of a lens from the center of a chip to its edge to obtain uniform sensitivity as a whole.
2. Discussion of the Related Art
Research to increase the photo sensitivity in manufacturing an image sensor is on going. One example of such research is the light-condensing technology.
For example, an effort for increasing the fill factor (the ratio of a light-receiving portion to the whole image sensor area) is being made to improve the photo sensitivity in a CMOS image sensor having a light-receiving portion for sensing the light and a CMOS logic circuit part where the sensed light is converted to an electric signal to be used as data.
The problem awaiting solution, other than a matter of the fill factor in the light-condensing technology, is to overcome the sensitivity difference between areas according to the incident angle.
This is a critical factor that determines the quality of the equipment required for an extreme near-by pick-up.
A micro lens construction of a related art image sensor and the photo sensitivity between areas according to light incident angles will be described with reference to the accompanying drawings.
FIG. 1 is a sectional block diagram of a related art image-sensor, and FIGS. 2A and 2B are block diagrams; illustrating respective light paths in the case of a long-distance pick-up and a near-by pick-up.
In the related art, a micro lens used in a CCD or CMOS image sensor controls the light path and increases the total amount of the light received.
In other words, in the related art, micro lenses formed on one chip have the same shape and size as one another.
As shown in FIG. 1, a micro chip 13 has micro lenses 12 which are positioned above light-receiving portions 11 and respectively corresponding to them. Every micro lens 12 has the same diameter ‘III’ and the same height ‘I ’.
That is, the micro lenses are formed with an identical size whether they are on the center part of the chip or on the edge of the chip.
Also, the light-receiving portions 11 are designed in such a way that they have the same size ‘II’ as one another and the distance ‘IV’ between the respective light-receiving portions 11 is uniform whether they are on the center part of the chip or on the edge of the chip.
The distance ‘V’ between the micro lenses 12 is designed to be uniform as well.
In the related art image sensor, the incident angle of the light depends on the position of a chip. Also, the photo sensitivity deteriorates as the incident angle is maximized in case of an extreme near-by pick-up.
FIG. 2A is a block diagram illustrating a long distance pick-up. As shown in FIG. 2A, the incident angle of the light has different degrees as a chip is differently positioned.
FIG. 2B is a block diagram illustrating an extreme near-by pick-up. As shown in FIG. 2B, the incident angle is maximized at the edge of a chip
A path of the light started from an object 15 is focused by passing through a lens 14 and it has different incident angles on the center part of the image sensor chip 13 compared to the edge of the chip.
That is, as shown in FIG. 2A, the incident angle 01 at the edge of the image sensor chip is bigger than the incident angle 02 on the center part of the chip. Also, as shown in FIG. 2B the incident angle 03 at the edge of the image sensor chip is bigger than the incident angle 04 on the center part of the chip.
The change of the incident angle is more noticeable in the case of a near-by pick-up (FIG. 2). Thus, even on the same area of the chip, the light incident angle 04 is bigger than 02, and the light incident 03 is bigger than 01.
At this instance, on the part that the incident 03 is positioned and on its neighboring pixels, the incident angle becomes much bigger such that the pick-up of the object is difficult as the incident angle falls out of a permissible range.
Since the incident angle differs as its location on the chip changes, sensitivity of the light differs on the respective light-receiving portions.
The related art image sensor has a number of limitations as follows:
First, because the micro lenses are identically designed despite the difference in the light incident angles according to different chip areas a difference in the photo sensitivity occurs in these areas.
Second, the pick-up or decoding of information may be impossible. Even though the unevenness caused by the photosensitivity difference in case of a general pick-up is invisible to the naked eye, when equipments required for an extreme near-by pick-up (e.g., equipments required for a pick-up/detection of dot code) are used, the characteristic differences caused by the photo sensitivity difference are very big such that, a pick-up or decoding of information is impossible.